CODEWITHSUNDEEP
javascriptasync-await
Max
Max

Reputation: 104

How to await a recursive method call in javascript

I am trying to await a recursive method call in javascript. This is my code to start the recursive method:

(async function start() {
    await writeText(htmlEditor, 0, time, '#editor');
    await writeText(fileSystem, 0, time, '#fileSystem');
    await console.log("Hello World");
}).call(this);

This is the recursive method:

function writeText(message, index, interval, to) {
    return new Promise(resolve => {
        let pre;
        if (index < message.length) {
            pre = document.getElementById('editor');
            pre.scrollTop = pre.scrollHeight;
            writeChar(message[index++], to);
            setTimeout( function () {
                writeText(message, index, interval, to);
            }, time);
        }
    })

}

However, when I use this code, all methods in the start function are called at the same time. I suspect that this is because of the recursive call in the writeText function.

How can I wait for the whole recursive stack to be finished?

Upvotes: 0

Views: 115

Answers (1)

CollinD
CollinD

Reputation: 7573

Your writeText function doesn't do any work to give consumers a hook into when execution is actually completed. setTimeout is used to do a kind of "fire-and-forget" type of execution here.

Try having it return a promise that resolves when the work is actually done:

function writeText(message, index, interval, to) {

    let pre;
    if (index < message.length) {
        pre = document.getElementById('editor');
        pre.scrollTop = pre.scrollHeight;
        writeChar(message[index++], to);
        // wrap the setTimeout in a promise and proxy the result of the recursive call
        return new Promise((resolve, reject) => {
            setTimeout( function () {
                writeText(message, index, interval, to).then(resolve, reject);
            }, time);
        });
    }
    // "base case" I guess, return undefined
    return Promise.resolve();
}

Upvotes: 2

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